This is a continuation-in-part application of Ser. No. 513,683, filed Oct. 10, 1974, and now abandoned.
This invention relates to the art of electrostatographic copying and more specifically to a novel method for the preparation of a novel photosensitive device.
In the art of electrostatographic copying, a plate comprising a photoconductive insulating layer is electrostatically charged in the dark in order to apply a uniform charge to its surface. The charged plate is then exposed to activating radiation in imagewise configuration to selectively dissipate the charge in the illuminated areas while leaving behind a latent electrostatic image corresponding to the non-illuminated areas. This latent image is then developed by depositing a finely divided electroscopic marking material on the surface of the plate. This concept, which was originally disclosed by Carlson in U.S. Pat. No. 2,297,691, has been further amplified in many related patents in the field.
Conventional xerographic plates usually comprise a photoconductive insulating layer overlaying a conductive substrate. A photoconductive material which has been widely used as a reusable photoconductor in commercial xerography comprises amorphous selenium.
An improved type of photoreceptor useful in xerographic copying comprises an electrically conductive substrate having on its surface a relatively thin layer of photoconductive material overcoated with a relatively thick layer of an organic active transport material. This type of photoreceptor is advantageous due to its increased flexibility and the protection from physical damage afforded the photoconductor by the layer of active transport material. In addition, this configuration facilitates the use of photoconductors that are too conductive in the dark for use in conventional photoreceptors. The usual method of preparing such a photoreceptor involves applying the layer of photoconductive material to the substrate (such as by the vapor deposition of selenium) and then applying a solution of the organic active transport material to the photoconductive surface. Evaporation of the solvent, which is normally carried out at an elevated temperature, leaves an adherent, continuous layer of the active transport material. This method of fabrication provides a finished photoreceptor which is subject to internal strains and stresses which may cause the active transport layer and/or photoconductive layer to peel away from the rest of the structure. This is the case because the volume of the active transport material is reduced during drying thereby setting up internal strains in the layer. Also, the different coefficients of thermal expansion of the substrate, photoconductor and active transport material lead to additional structural strain at the elevated temperatures normally employed for solvent removal. In addition, thermal shock may further strain the system when the structure is removed from the drying oven. Since the film of organic transport material is constrained on one side due to its being in contact with the photoconductive layer on the substrate, these strains in the organic material are not adequately relieved. The strains thus created often lead to mechanical failure of the photoreceptor.
It would be desirable, and it is an object of the present invention, to provide a novel method for the preparation of an electrostatographic photoreceptor comprising a conductive substrate, a relatively thin layer of a photoconductive material and a relatively thick layer of an organic active transport material overcoating the photoconductive layer.
A further object is to provide such a process in which the photoreceptor prepared is not subject to internal strains resulting in its mechanical failure.
Another object is to provide such a process which can be conveniently carried out in conventional equipment.